If I could pick one to be found, it would be literally any of the monster Mycenaean burials — but it’s likely that all of those were known to the locals, and plundered a 100 generations back. Ah well.
There’s at least one unknown tomb in the Valley of the Kings, the entrance to which was discovered by accident during the clearing of another of the unknown tombs — apparently the entrance had (like that of Tut’s) been obscured by a slightly more recent tomb construction, with the tailings tipped over its opening.
Then it was ignored and covered over again. The tomb site may have been high enough above the valley floor that it hasn’t been destroyed by either tourist traffic or flash floods. It probably isn’t going to be a pharaoh’s, but it will probably be sumptious.
Nor will it be Nefertiti’s, apparently that was found by local yokels in the late 19th c, when some artifacts which clearly came from her burial entered the market.
Probably any Mycenaean tombs on the scale of the largest tholos tombs at Mycenae would have been discovered already, but the tholos tombs come in various sizes and possibly more could be found. Additional Minoan or Mycenaean palaces could await discovery. What would be really nice to find would be a cache of Linear B tablets with the name of a ruling monarch—particularly if it matched one known from Greek mythology. King Agamemnon giving orders for quantities of supplies to be assembled at Aulis for the voyage to Troy?